1. Field
Embodiments of the present disclosure pertain to resin infusion processes and, in particular, to resin infusion processes for the fabrication of fiber reinforced composites employing vacuum pressure processing.
2. Description of the Related Art
Fiber-reinforced polymer matrix composites (PMCs) are high-performance structural materials that are commonly used in applications requiring resistance to aggressive environments, high strength, and/or low weight. Examples of such applications include aircraft components (e.g. tails, wings, fuselages, propellers), boat hulls, and bicycle frames. PMCs comprise layers of fibers that are bonded together with a matrix material, such as a polymer resin. The fibers reinforce the matrix, bearing the majority of the load supported by the composite, while the matrix bears a minority portion of the load supported by the composite and also transfers load from broken fibers to intact fibers. In this manner, PMCs may support greater loads than either the matrix or fiber may support alone. Furthermore, by tailoring the reinforcing fibers in a particular geometry or orientation, the composite can be efficiently designed to minimize weight and volume.
Numerous processes have been developed for the manufacture of PMCs. Examples may include wet layup, prepregging, and liquid infusion. In wet layup, the reinforcing fiber is wet with the matrix material, placed into a mold cavity, and allowed to harden or cure. This process may be performed in an automated fashion, such as with a chopper gun or a machine that receives dry fiber rolls, runs them through a resin dip bath, and places the wetted fibers in the mold. Alternatively, the resin may be applied manually using brushes.
In prepregging, composite components are fabricated with pre-impregnated woven fabrics or prepregs. The reinforcing fibers are impregnated with the matrix resin in a controlled fashion and frozen in order to inhibit polymerization of the resin. The frozen prepregs are then shipped and stored in the frozen condition until needed. When manufacturing composite parts from prepregs, the prepregs are, thawed to room temperature, cut to size, and placed in the mold cavity. Once in place, the prepregs are vacuum bagged and cured under pressure to achieve the required fiber volume fraction with a minimum of voids.
In liquid infusion processing, the reinforcing fibers are placed within a mold cavity or other mechanism for net-shape tooling in dry conditions, wetted with the matrix resin, and cured. Liquid infusion processing may be accomplished by a variety of techniques, including high and low pressure resin transfer molding (RTM), Resin Film Infusion (RFI), vacuum assisted resin transfer molding (VARTM), pultrusion, hyper VARTM, Seeman composite resin infusion molding process (SCRIMP®), reaction injection molding (RIM) or same qualified resin transfer molding (SQUIRTM).
Each of these processes may be problematic, however. While relatively inexpensive, wet layup fabrication typically produces composites having low fiber volume fractions and high porosity, which reduce the overall strength and quality of the composite so manufactured. In contrast, while fabrication of composites through prepregging can achieve higher fiber volume fractions and reduced void content, the cost to fabricate prepregs is much higher. Furthermore, the shelf life of the frozen prepregs is limited, due to continued polymerization, even in the frozen state, and handling must be carefully controlled. Fabrication of composites by infusion and other closed mold processes, such as RTM, is also expensive, owing to the high cost to obtain and maintain the requisite tooling and liquid injection systems.